I am modelling a settling tank (in axisymmetric coordinates) with two scalars involved, i.e. settling solids and LiCl as tracer. The reason why I treat LiCl as a UDS is to account for density effects (and varying inlet conditions for flow rate and solids concentration) when you introduce it as a pulse.

When I inject this UDS with both fixed concentration and velocity, it seems that the tracer is convected too slowly compared to the velocity imposed at the boundary. In the UDF tracer convection is described with F_FLUX.

Has anybody the same problem? Or does anyone have suggestions what could have gone wrong?